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Bronchodilators |   |
Epinephrine (Adrenalin, Bronkaid, Primatene) is often held up as the standard against which other sympathomimetics are judged. It is a powerful bronchodilator and decongestant that can be administered by injection or by aerosol, and an agent that causes an increase in the rate and force of heart contractions, dilation of the bronchial smooth muscles, and constriction of the peripheral vasculature. It is used parenterally for the relief of acute bronchial asthma. In the hospital setting, epinephrine is used frequently for its effect on the circulation, during cardiopulmonary resuscitation (CPR), and to combat allergic reactions.
Racemic Epinephrine (MicroNephrin, Vaponefrin) is a synthetic form of naturally occurring epinephrine. It is less potent than epinephrine, has fewer side effects, yet can achieve reasonable bronchodilation. It is primarilly recommended for croup (laryngotracheobronchitis), laryngeal edema, and appears to be useful in recently extubated patients due to its decongestant action. The usual aerosol dose is 0.25 cc to 0.5 cc in 2-3 cc NS Q4 hours. For patients younger than two years old, the recommended dose is 0.1 to 0.25 cc.
Ephedrine (Tedral, Marax, Primatene, Quadrinal) is an alkaloid derived from an herb by the Chinese over 5,000 years ago. It demonstrates similar to the action as epinephrine, but it isn't used regularly for bronchodilation. It is one of the few Beta adrenergic agonists effective when given orally. It is considered long-acting (four to six hours) and slightly less potent than epinephrine. Tablets are the usual method of administration. The tablets also contain theophylline.
Ephedrine is a potent CNS stimulant so a tranquilizer is often added. Tachyphylaxis readily develops with ephedrine, along with excessive CNS stimulation. Excessive use by patients can cause marked mental excitation and elevation of blood pressure. Dosage varies depending upon the patient's condition. Proprietary preparations contain between 12-25 mg of ephedrine with 50-130 mg of theophylline.
Isoproterenol (Isuprel) a powerful beta stimulator, both beta1 and beta2, is somewhat better bronchodilator than epinephrine, with nearly complete absence of vasopressor activity. However, its strong beta1 effects increase the probability of tachycardia, thereby limiting the frequency of its use. It is available in aqueous concentrations of 1:100 and 1:200, with the latter being the strength recommended for aerosol therapy. For short term therapy, two to four inhalations at four hour intervals is normal. Long term therapy mandates further dilution of the concentrate.
Metaproterenol (Metaprel, Alupent) a derivative of isoproterenol, it has significantly longer duration of action, and has beta1 effects when given by inhalation. Metproterenol can be taken orally or inhaled, but is contraindicated in patients with pre-existing cardiac arrhythmias, and used extremely cautiously in patients with hypertension, coronary artery disease, congestive heart failure, hyperthyroidism, and diabetes.
Isoetharine (Bronkosol, Bronkometer) has a strong Beta2 effect with minimal Beta1 stimulation. Both of these effects are less than those of isoproterenol. Isoetharine is administered orally or by MDI, SVN, IPPB. it is reportedly more effective in conditions characterized by diffuse bronchospasm, as in bronchial asthma, than in those with obstructing secretions, as in chronic bronchitis. Duration of action is 2 to 4 hours. The usual aerosol dose of 0.5 cc of the 1% solution in 2-3 cc NS Q4 hours may be increased to 1 cc for severe bronchospasm.
Terbutaline (Bricanyl, Brethine, Brethaire) acts directly on beta2 receptors, has minimal beta1 effects, and is more potent and long-acting than metaproterenol. Inhaled terbutaline has been shown to increase mucociliary clearance by as much as 50%. It is also available for oral and subcutaneous administration.
Albuterol (Proventil, Ventolin) is one of the most commonly used aerosolized beta2 adrenergic bronchodilators, but is also effective orally or intravenously. The aerosolized form causes fewer side effects, and it is long acting because it is not metabolized by COMT. The normal dosage when delivered by a small volume nebulizer is 2.5 mg QID. A sustained released form of albuterol is available as either Proventil Retabs or Volmax, and the extended activity lasts up to 12 hours.
Pirbuterol (Maxair) is a selective beta2 adrenergic bronchodilator similar to albuterol, and is long-acting with a duration of action of about 5 hours. It is effective when aerosolized or given orally. Effective onset of action occurs within 15 minutes, with peak effectiveness being realized within an hour. Recommended dose for adults and children older than 12 is 0.4 mg, inhaled 2 or 3 times every 4-6 hours.
Fenoterol is one of the newer beta adrenergic bronchodilators (although it has been used in Europe for some time). Fenoterol is available for oral or inhalation administration, and appears to have a very long duration of action (8 hours), with minimal Beta1 impact. Fenoterol has the advantage of acting mainly on the peripheral airways, and its bronchodilation is proportional to isoproterenol. On the other hand, it has more side effects than seen with albuterol or terbutaline, and has been associated with an increase in morbidity and mortality.
Bitolterol (Tornalate) is known as a pro-drug, meaning that the administered form must be converted in the body to become an active drug. Since the process of activation begins when the drug is administered and gradually continues over time, duration of action is prolonged to about 8 hours. It has been compared favorably with albuterol, and has fewer side effects than fenoterol with similar in duration of action. Each activation of the MDI delivers about 0.37 mg of bitolterol, and recommended dosage is 2 puffs every 8 hours with maximum dosage not to exceed 2 puffs every 4 hours.
Salmeterol Xinafoate (Serevent) received FDA approval in 1994, and represents a new generation of long-acting beta2 specific bronchodilators whose pharmakinetics provide for a slower onset and time to peak effect, and a longer duration of action than seen in other adrenergic agents. It is indicated for long-term maintenance therapy of asthma which cannot be controlled by occasional use of beta agonists, and for the prevention of bronchospasm in patients needing maintenance therapy for reversible airway obstruction. Dosage as an MDI is 2 puffs (42mcg) Q12 hours, and its side effects and safety profile are similar to other bronchodilators.
Formoterol is a catecholamine analogue with beta2-selective action. It is similar to salmeterol in its long-acting effectiveness of about 12 hours, maintaining FEV1 values 20% above baseline in patients with stable asthma. Dosage is the same as salmeterol, simplifying administration for asthmatics.